NTSB Identification: ANC99FA021.
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Nonscheduled 14 CFR
Accident occurred Sunday, January 10, 1999 in QUINHAGAK, AK
Probable Cause Approval Date: 03/31/2000
Aircraft: Cessna 207, registration: N6312H
Injuries: 1 Minor.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The certificated commercial pilot reported that during the initial descent to land, the engine began to run rough and lose power. He noted that the roughness improved momentarily, followed by a severe engine vibration, and complete loss of engine power. The pilot selected a forced landing area on snow and tree-covered terrain. The airplane sustained substantial damage to the landing gear, fuselage, and wings. Postaccident investigation discovered that the engine crankshaft had sustained a complete fracture of the #2 cheek. A subsequent investigation revealed that on some crankshafts, a crack in the nitride layer that originated from a shallow tool mark, would in some cases ultimately lead to the fatigue failure of the crankshaft cheek. On April 22, 1999, the FAA issued an emergency airworthiness directive (AD) requiring that all TCM 470, 520, and 550 engine crankshafts manufactured in 1998, with less than 300 hours in service, will be inspected in accordance with the TCM critical service bulletin (CSB) within 10 hours of operation.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

Loss of engine power due to fracture of the engine crankshaft, and the manufacturer's improper manufacturing procedure during engine assembly. Factors associated with the accident were the manufacturer's inadequate quality control standards, trees, and snow-covered terrain.

Full narrative available

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